nuclear lecture

8/12/2019 Nuclear Lecture

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Nuclear ChemistryChemistry I Chapter 25

Chemistry I Honors

Chapter 19

ICP Chapter 18

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Radioactivity

One of the pieces of evidence for the

fact that atoms are made of smaller

particles came from the work of

________ (1876-1934). She discovered________, the

spontaneous disintegration of some

elements into smaller pieces.


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3Nuclear Reactions vs.Normal Chemical Changes

Nuclear reactions involve the nucleus The nucleus opens, and protons and

neutrons are rearranged

The opening of the nucleus releases atremendous amount of energy that holdsthe nucleus togethercalled bindingenergy

Normal Chemical Reactions involveelectrons, not protons and neutrons


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Mass Defect

Some of the mass can be converted into

energy

Shown by a very famous equation!

E=mc2

Energy

Mass

Speed of light


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Types of Radiation

e0

1

He4

2

Alpha ()a positively

charged helium isotope - weusually ignore the charge because it involves

electrons, not protons and neutrons

Beta ()an electron

Gamma ()pure energy;

called a ray rather than a

particle

0

0


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Other Nuclear Particles

e0

1

n1

0Neutron

Positrona positiveelectron

Protonusually referred to

as hydrogen-1

Any other elemental isotope

H

1

1


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Penetrating Ability


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Balancing Nuclear Reactions

In the reactants(starting materials

on the left side of an equation) and

products(final productson the right

side of an equation)

Atomic numbers must balance

and

Mass numbers must balance

Use a particle or isotope to fill in the

missing protons and neutrons


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Nuclear Reactions

Alpha emission

Note that mass number (A) goes downby 4

and atomic number (Z) goes downby 2.

Nucleons (nuclear particles protons and

neutrons) are rearranged but conserved


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Nuclear Reactions

Beta emission

Note that mass number (A) is unchanged

and atomic number (Z) goes up by 1.


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Other Types of Nuclear Reactions

Positron (0

+1): a positive electron

Electron capture: the capture of an electron

207 207


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Learning Check

What radioactive isotope is produced in the

following bombardment of boron?

10B + 4He ? + 1n

5 2 0


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Write Nuclear Equations!

Write the nuclear equation for the beta

emitter Co-60.


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Artificial Nuclear Reactions

New elements or new isotopes of known elements

are produced by bombarding an atom with a

subatomic particle such as a proton or neutron

-- or even a much heavier particle such as4

Heand 11B.

Reactions using neutrons are called

reactionsbecause a ray is usuallyemitted.Radioisotopes used in medicine are often made byreactions.


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Artificial Nuclear Reactions

Example of a reactionis productionof radioactive 31P for use in studies of P

uptake in the body.

3115P +

10n --->

3215P +


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Transuranium Elements

Elements beyond 92 (transuranium)made

starting with an reaction238

92U +1

0n --->239

92U + 239

92U --->239

93Np +0

-1239

93Np --->239

94Pu +0

-1


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Nuclear Fission


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Nuclear Fission

Fission is the splitting of atomsThese are usually very large, so that they are not as stable

Fission chain has three general steps:

1. Initiation. Reaction of a single atom starts the

chain (e.g., 235U + neutron)

2. Propagation. 236U fission releases neutrons that

initiate other fissions

3. ___________ .


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Stability

of Nuclei

Out of > 300 stable isotopes:

Even Odd

Odd

Even

ZN

157 52

50 5

3115P

199F

21H,

63Li,

105B,

147N,

18073Ta


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20Band of Stabilityand Radioactive

Decay


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21Representation of a fission process.


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Nuclear Fission & POWER

Currently about 103

nuclear power plants in

the U.S. and about 435

worldwide.

17% of the worlds

energy comes from

nuclear.


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23Figure 19.6:Diagram of a nuclear power plant.


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Nuclear Fusion

Fusionsmall nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy


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Nuclear Fusion

Fusion

Excessive heat can not be contained Attempts at cold fusion have

FAILED.

Hot fusion is difficult to contain


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Half-Life HALF-LIFEis the time that it takes for

1/2 a sample to decompose. The rate of a nuclear transformation

depends only on the reactant

concentration.


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Half-Life

Decay of 20.0 mg of 15O. What remains after 3 half-lives?

After 5 half-lives?


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Kinetics of Radioactive Decay

For each duration (half-life), one half of the

substance decomposes.

For example: Ra-234 has a half-life of 3.6 days

If you start with 50 grams of Ra-234

After 3.6 days > 25 grams

After 7.2 days > 12.5 grams

After 10.8 days > 6.25 grams


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Learning Check!

The half life of I-123 is 13 hr. How much of

a 64 mg sample of I-123 is left after 39

hours?


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Effects of Radiation


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Geiger Counter

Used to detect radioactive substances


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Radiocarbon Dating

Radioactive C-14 is formed in the upper atmosphereby nuclear reactions initiated by neutrons in

cosmic radiation

14N + 1on --->14C + 1H

The C-14 is oxidized to CO2, which circulates

through the biosphere.

When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with t1/2= 5730years.

Activity of a sample can be used to date the sample.

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Nuclear Medicine: Imaging

Thyroid imaging using Tc-99m

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Food Irradiation

Food can be irradiated with rays from60Co or 137Cs.Irradiated milk has a shelf life of 3 mo.

without refrigeration.USDA has approved irradiation of meats

and eggs.

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